Polymeric organic materials are widely used in all types of energetic formulations, primarily as either fuels or combustible binders. During the formulation of plastic bonded explosives, the hazard characteristics of all but the most insensitive of high explosives can be greatly improved by the addition of a suitable binder. However, whilst the addition of such a binder desensitises the explosive, if the binder is inert and, has a lower density than the filler, it inevitably detracts from the performance. The tendency when formulating explosives is therefore to maximise solids loading in order to enhance performance. In contrast, larger quantities of binder are most beneficial in optimising safety. One way of improving these conflicting requirements is to use an energetic binder.
Energetic binders can still be effective in desensitising the explosive but are also able to contribute to the overall energy of the system. The consequence of this is that they can be used in somewhat larger proportions than an inert binder, whilst retaining, or even increasing, the overall energy of the system. Given that energetic polymers may be intrinsically less sensitive, enhanced quantities of these materials may benefit charge safety by two separate mechanisms: (1) through the attainment of reduced solids loading and (2) because of the intrinsic insensitively of the material being added. Thus, as the binder loading is increased, a non-detonable energetic binder is effectively replacing a proportion of the detonable crystalline filler. The term ‘energetic polymer’ is normally used to describe macro molecules which contain energetic functionalities such as nitrato, nitro or azido groups.
The difficulty with energetic binders is to obtain materials which combine high energy-density with peak physical properties and ignition properties. Existing examples of energetic binders comprise glycidyl azide polymer (GAP), poly (3-methyl-3-nitratomethyl oxetane) (polyNIMMO) and polyglycidyl nitrate (polyGLYN).
The application of laser ignition to energetic materials potentially offers a number of advantages, including circumvention of electrostatic sensitivity issues and avoidance of the need to use high sensitivity (e.g. primary explosive) ingredients. Although high power UV or IR lasers can be effective at directly igniting energetic materials, such lasers tend to be unattractive for application to weapon systems due to their relatively high cost, large size and energy requirements. Near-IR (NIR) diode lasers represent a practical solution for this type of application. Thus small NIR diode lasers operating at modest power levels are both cheap and readily available.
However, organic energetic materials, including energetic binders, tend to show little absorption in this wave band and therefore respond poorly to the radiation from such lasers. This problem has been addressed through the addition of Carbon Black (CB) to the energetic material to enhance its optical absorption. But such addition is inconvenient and can increase processing costs, reduce the energy density available from the formulation and potentially modify its combustion characteristics in an adverse fashion. Also the consequences of CB addition can be difficult to predict, because they are dependent upon various factors including the relative physical characteristics of the CB and the energetic material.
It is an object of the invention to provide polyphosphazenes which overcome or mitigate at least one of the above problems and/or another problem associated with the prior art.